Elastomeric fibers, such as those made from polyurethane, are suitable for fibers and fabrics due to their outstanding stretch and recovery properties. However, certain polyurethane filaments are very tacky compared to conventional textile filaments, such as those melt-spun from nylon or polyester polymers. These polyurethane filaments tend to stick to each other, especially when wound on a pirn, bobbin, cake or other such yarn package. Tackiness can manifest itself in fused filament segments and high yarn-to-yarn friction. Also, on being unwound from a yarn package, the polyurethane filaments can experience excessive tension and large, rapid transient increases in tension, which in turn lead to many broken filaments during operations such as covering, knitting, weaving and the like. Further, because the polyurethane filaments are subjected to higher compressive forces when they are located in the inner layers of a wound up yarn package, as compared to the compressive forces on the filaments in the outer layers, average tension and numbers of tension transients can change significantly as the filaments are unwound from the yarn package. Such tension variations produce nonuniformities in fabrics made with fibers produced from polyurethane supplied from such packages. Tack between fibers is known to increase with aging on the package form. In addition to time, higher than ambient storage temperatures can accelerate the increase in tack thus limiting the ability to remove fiber from the package in knitting or other fabric forming processes. Thus agents that slow this increasing tack are desired for extended usefulness of fiber stored on the package. Polyurethane films can also exhibit similar problems as the result of tackiness.
To reduce tackiness certain additives have been introduced into polyurethane fiber, such as spandex. These additives include silicon oil and metal stearates. In addition, various finishes have been suggested for lubricating the surfaces of the fiber and thus reducing the tackiness of spandex. However, further improvements are desired.
In addition to the tack problem, certain polyurethane filaments are not easily dyeable as compared to conventional textile filaments, such as those melt-spun from nylon or polyester. Other polyurethane filaments may accept dye, but the dye tends to wash out readily. Spandex is often covered or blended with other fibers such as those made from polyamide, i.e. nylon, and polyester. However, when such fibers and fabrics are stretched, the undyed or slightly stained spandex shows through the colored fiber covering. This is referred to as "grin through".
In addition, the spandex reflects visible light causing a glitter effect. Both "grin through" and glitter are objectionable in most dyed fabrics. Polyurethane film can also be difficult to dye.
An object of the present invention is to provide improved polyurethane fibers, and fabrics made therefrom, and films that possess reduced tack and processes for providing such fibers. Another object of the present invention is to provide improved polyurethane fibers, fabrics, and films that permit enhanced dyeability and washfastness. A further object of the present invention is to provide processes which increase the ability to provide dyed fiber and films. These improvements will permit more efficient utilization of the fiber in yarn and fabric making operations and the film in other applications, such as coatings, while retaining other desirable elastomeric properties.